Upgrade engine version to resolve inconsistent percentage split evaluations (#61)

* Upgrade engine version

* Revert git pinned flag engine version

Author: matthewelwell

requirements.txt

@@ -18,7 +18,7 @@ click==8.0.3
     # via uvicorn
 fastapi==0.81.0
     # via -r requirements.in
-flagsmith-flag-engine==3.5.0
+flagsmith-flag-engine==3.6.0
     # via -r requirements.in
 h11==0.12.0
     # via uvicorn